how will ethanol affect my fuel mileage ?

If I understand correctly, The fuel mileage loss depends on your build. Higher compression engines run the e85 more efficiently than the lower compression engines. I have no experience and its been a while since i read about it. One of these I'll have the money to build an engine and get some learning experience on it for myself. Hoping someone that knows for a fact whether or not this is true will chime in and say so. Im sure Im not the only one that would enjoy seeing all the ducks in a row